We have developed a hormonal treatment that allows the induction of differentiation in teratocarcinoma stem cells in two stages: retrinoic acid treatment yields an altered, stable phenotype and further treatment with dibutyryl cAMP results in the generation of cell type indistinguishable from definitive embryonic parietal endoderm. these differentiated cells produce copious quantities of Type IV collagen, laminin, and plasminogen activator, in contrast to the stem cells which produce little if any on these proteins. We propose to use this system to begin investigations of gene regulation in early embryonic cells. We have prepared to cDNA library from the differentiated cells, and will isolate from this library clones containing cDNAs related to these 3 proteins. We will then use the probes to: 1) explore the regulation of expression of these during differentiation; 2) examine the gene and chromatin structure for the proteins in the stem cells and differentiated cells; 3) analyze the early mouse embryo for the nature and regulation of expression of these genes. Other colonies present in the cDNA library may also be useful both for exploring how the synthesis of certain RNA sequences present most abundantly in the stem cells in regulated, and also for investigating the function of these RNA molecules.